session values is nill,or missing session values,or session values are reset

values you are setting to session are domain specific.ie if you set a value  session[:value]=5 when u are in localhost, this value will not get if you are in the ip address of your localhost.

means you set a session value when you are in localhost and u redirect you appication to some other site say twitter for twitter integration, then you given your callback url to your the ip address of you localhost.that time you will not get the value you set in localhost.because you are in a different domain.

you can retrive session values that is set in the same domain.localhost and its ip address are considered different domain as far as sessions are considered.